Well known is the type of bird feeder comprising side walls attached together and to a bottom wall and projecting above the bottom wall to define a cavity adapted to contain a supply of bird feed, with the bottom wall including at least one tray portion extending past an outer surface of one of the side walls and having fixed thereon an edge wall at a position spaced from that side wall to help define a shallow feeding tray between that side wall and the edge wall. Typically the walls define a passageway between the cavity and the feeding tray to afford the flow of bird feed from the cavity to a shallow recess in the feeding tray. Such bird feeders also include perch means (which may be provided by the upper edge of the edge wall or by an elongate perch bar fixed in spaced generally parallel relationship along the edge wall) for allowing birds to perch along the edge wall facing the feeding tray while they eat.
While such bird feeders are effective in dispensing bird feed, certain types of birds (particularly ground feeding birds such a sparrows and grackles) have a tendency to throw or scatter bird feed from the tray by swinging their beaks from side to side within the tray so that significant amounts of bird feed can be wasted. Also, strong winds can blow birdseed out of such feeders and onto the ground, resulting in wasted feed.